1. Field of the Invention
The present invention relates to an aberration-correcting optical system, a projection exposure apparatus, and a device manufacturing method, and more particularly, to an aberration-correcting optical system, a projection exposure apparatus used in manufacturing a semiconductor chip such as an IC and an LSI, an image pickup device such as a CCD and a display device such as a liquid crystal panel, and a device manufacturing method.
2. Description of the Related Art
In a scanning type exposure apparatus, since the cross section of illumination rays for illuminating a mask is shaped like a rectangle or an arc which extends in an orthogonal direction orthogonal to the scanning direction, the cross section of imaging rays produced from a mask pattern also extends in the orthogonal direction. If such imaging rays enter a projection optical system (a system composed of lenses or a combination system of lenses and mirrors), the lenses in the projection optical system absorb part of the imaging rays, and this causes the refractive index distribution and the deformation condition of a refracted plane in the scanning direction to differ from those in the orthogonal direction. Therefore, the best focal position (best imaging position) in a pattern in which the illumination rays are diffracted mainly in the scanning direction and the diffracted rays are made incident on the projection optical system differs from that in a pattern in which the illumination rays are diffracted mainly in the orthogonal direction and the diffracted rays are made incident on the projection optical system (this difference is hereinafter referred to as "astigmatism").
In order to solve the above problem, the applicant of this application proposes in Japanese Patent Laid-Open No. 8-008178 that a heating means for heating a projection optical system should be placed so that the refractive index distribution of the lens and the deformation condition of the refracted plane in the scanning direction is almost equal to those in the orthogonal direction.